I'd take a dodgy, dancing car-dealer over the Prince of Wales any day

It is hard to imagine a greater waste of police time than trailing round London after Wallis Simpson, the woman who had an affair with and subsequently married King Edward VIII. Special Branch files released by the Public Records Office contain the startling revelation that she once visited an antique shop in South Kensington with the Prince of Wales, as he then was, and the couple appeared to be "on very affectionate terms". A police spy then interrogated the shopkeeper, who confirmed his worst fears by volunteering that "the lady seems to have POW completely under her thumb".

Special Branch might well have responded that, in their considered opinion, Mrs Simpson was no lady. She was "regarded as a person very fond of the company of men", an observation that exposes the contempt in which she was held by the British establishment and its functionaries. After complaining that the identity of Mrs Simpson's "secret lover" had not yet been established, the snoopers could barely contain their excitement when he was discovered to be Guy Marcus Trundle, a car dealer with an address in Mayfair.

The appearance of the felicitously named Mr Trundle is the one bright spot in a story whose leitmotifs are snobbery, double standards and prurience. Special Branch also compiled files on Mrs Simpson's friends, describing Lady Emerald Cunard with breathtaking racism as "the mother of the notorious Nancy Cunard, who is very partial to coloured men". Mrs Simpson herself, according to this version, was a ruthless gold-digger who employed techniques she had learnt in an Eastern brothel – the famous Singapore grip – to ensnare a naive and trusting Prince, while simultaneously cuckolding him.

Exponents of this theory must have been disappointed when the 100 files released last week failed to include the notorious "China dossier" on Mrs Simpson's sex life in the 1920s. It is quite likely that no such file exists, being the stuff of misogynist fantasies, but it was supposed to document the techniques that helped her, uniquely among the Prince's lovers, to compensate for his, ahem, shortcomings. The proposition that the Prince and his younger brother, later King George VI, suffered from similar sexual problems is taken seriously by royal biographers; at the Dartington literary festival last summer, a chance remark of mine sparked an animated discussion on this very subject between my friend Robert Lacey and Sarah Bradford, authorities in the field. I can't remember whether the words "turkey baster" were actually used, but it was a choice example of what Private Eye calls "royal balls".

Anyway, the point I am making is that Mrs Simpson has been the victim of a long-running – and, it now transpires, publicly funded – smear campaign. "She was game for anything," The Daily Telegraph declared on Friday, adding that the newly released files confirm her reputation as a "duplicitous nymphomaniac". Yet for anyone not blinded by royal mystique, there is a very different way of looking at all this.

I don't know if little girls still hum "Some Day My Prince Will Come" but there is a plausible case to be made that Mrs Simpson's tragedy – like that of Diana, Princess of Wales – is that her wish came true. The stylish American who simply did what impecunious women of her generation were supposed to do – make a good marriage or three – was condemned to live with a vain man who always wore a kilt to dinner, collected porcelain pugs, and was given to getting drunk and singing interminable German songs.

So thank god for Mr Trundle, who may be the last person with whom Mrs Simpson had a good time before embarking on a dull marriage. Special Branch officers described him as "a very charming adventurer" who admitted accepting money and gifts from Mrs Simpson. They were so disgusted by their own imputation that she paid him for sex that they barely registered his most important attribute: he was an "excellent" dancer. Now that – and I say this as someone who has spent years trying to coax husbands and lovers on to the dance floor – is worth its weight in gold. Even the most prejudiced spy should know that it takes two to tango.